Why does it hang?

I was working on a friend?s computer and hit a wall. It seems that when running Scandisk and/or Defrag the system locks up. When I hit ctrl-alt-del the task menu shows that neither application is (not responding.) It also won’t run hwinfo.exe.
Does anyone a clue as to what I can do now? I almost feel compelled to fdisk and format and reload Win98 SE. All advice would be appreciated.

Tracey
A+